The present invention relates to a single crystal growing apparatus suitable for a single crystal growing of compound semiconductor materials of groups III-V and II-VI such as GaAs, InP, and CdTe, in particular to a horizontal Bridgman single crystal growing apparatus utilizing a direct monitoring electric furnace capable of rapid heating to high temperature over than 1240.degree. C. and rapid cooling by an electric furnace having a cylindrical double quartz tube coated with gold film on the internal wall surface, and capable of maintaining an optimum single crystal growing condition by observing directly with naked eyes the whole process of single crystal growing.
A Bridgman single crystal growing apparatus had developed initially by Bridgman, P.W. of United States of America in 1925, and various researches have been carried out that utilizing the method as this from 1957. According to a basic principle of the horizontal Bridgman single crystal growing method, firstly a liquid state gallium (Ga) is disposed at a high temperature portion of the interior of a quartz reaction tube, at the same time a solid state arsenic (As) is disposed at a low temperature portion, thereafter the gallium arsenide is synthesized at a temperature over 1238.degree. C. which is a melting temperature of the gallium arsenide, while the quartz reaction tube containing the melt of gallium arsenide is fixed, the growing furnace provided around the circumference of said quartz reaction tube is moved horizontally toward one direction along with the quartz reaction tube, thereby a single crystal can be grown by solidifying slowly from one end portion of the melt.
[Refer to : Bridgman, P.W., Proc. Amer. Acad. Sci.
60, 305 (1925),
Edmund, J.F. et al, Services Electronic
Research Laboratory Technical Journal 6,
123 (1957)]
In growing a single crystal with the Bridgman method as this, at first a contact between a seed crystal of gallium arsenide disposed into the interior of the quartz reaction tube and the melt of gallium arsenide is made, through this process a solidification becomes proceeded slowly in the direction of one way from said contacting portion as its starting point, at this moment, while maintaining the growing boundary interface formed between a solid state and a liquid state as a planar interface only by controlling precisely the growing temperature according to thereof, the manufacture of defect free gallium arsenide single crystal becomes possible.
Generally, in a horizontal Bridgman method or a liquid encapsulated Czochralski method, as a most dominant factor inducing a generation of dislocations in the case of single crystal growing, the instability of a crystal-melt interface during the solidifying process can be mentioned, this is because, in case where a seed crystal is surrounded with an incoherent state due to a surface tension of the melt upon contacting between a melt and a seed crystal so that a solidification arises first partly, fine twins or dislocations is produced from said portion.
Therefore, in case of a single crystal growing according to the seed crystal dipping of either a horizontal Bridgman method or a liquid encapsulated Czochralski method, it is possible to mention that whether or not how much the contact between a seed crystal and a melt being completely executed is a key for elimination of defect generation in the interior of the crystal.
And therefore, in case of a single crystal growing, while observing the process of series such as a contacting between a seed crystal and a melt being proceeded within inside of the quartz reaction tube and a formation of growing boundary interface, according to which a pertinent control becomes required, as a known observing method, following three methods may be cited:
(1) a method for forming a viewing window made of a quartz at
a side portion of the growing furnace [FIG. 1(A)],
(2) a method for measuring the temperatures by arranging a
number of thermocouples [FIG. 1(B)],
(3) a method for observing through an optical fiber [FIG. 1
(C)], and each observing method is explained as follows.
At first, in a crystal growing furnace in a method for observing the single crystal growing of the interior of a quartz reaction tube through a quartz viewing window, as shown in FIG. 1 (A), a boat 4 having a melt of gallium arsenide 2 and a seed crystal 3 is disposed into the high temperature portion of the cylindrical quartz reaction tube 1 and an arsenic 5 of solid state is encapsulated into the low temperature portion thereof, to a growing furnace 7 having a heater wire 6 wound on the outer circumference of the quartz reaction tube 1 there is formed with a quartz viewing window 8 for observing the growing process of a crystal at a side surface of a temperature portion being formed with a growing boundary interface. The reference numeral 9 is a thermocouple, and 10 is a quartz tube for a diffusion barrier.
However, in case of a method for observing the crystal growing process by making a quartz viewing window 8 as thus, since a symmetry of the cylindrical furnace 7 at the portion said quartz viewing window 8 being made is broken down and a nonuniformity of the temperature distribution arises at this portion, so that it causes the result that the crystal growing boundary interface is inclined or distorted and also exerts a bad effect to the temperature distribution of a melt state and a growing speed, therefore there has been a difficulty to obtain a complete single crystal without any crystal defect. Accordingly, though a few supplementary devices such as those utilizing either a reflection plate or a separate auxiliary furnace for solving the problems have been developed, these devices are not only complicated, but also it could not be expected the complete solution of said problems. Further, since a region possible to observe through the quartz viewing window 8 made at a wall of the crystal growing furnace 7 becomes observing only the extremely limited region proportional to the magnitude of the opening of said quartz viewing window 8 there has been a problem that the correct observation for said contacting location during the contacting process between a seed crystal and the melt of gallium arsenide is difficult.
[Refer to : Deyris, E : La Radiotechnique - compelec, France : French. Pat. No. 1494831.
L.R. Weisberg et al, J. Electrochem. Soc.
109 (1962) 642]
Next, according to a method utilizing the thermocouples, as shown in FIG. 1(B), in a crystal growing furnace 7 in which a quartz tube for a diffusion barrier 10 is disposed at an intermediate position, a boat 4 containing a seed crystal 3 and the melt of gallium arsenide 2 and an arsenic 5 of solid state are respectively disposed at each side thereof within the quartz reaction tube 1, and a heating pipe 6 of the electric furnace mounted around the circumference of said quartz reaction tube 1, which is the method for observing the temperature of the interior of a growing furnace 7 by arranging a number of thermocouples 9a, 9b for measurement within the interior of said quartz reaction tube 1, this method is advantageous in a view point that the uniform temperature distribution can be obtained within the growing furnace relative to the method observing through a quartz viewing window as aforementioned because it does not break the symmetry of the temperature distribution of the growing furnace 7, however the precise temperature control is possible only at a limited region adjacent that the contact of a seed crystal and the melt of gallium arsenide being carried out and the direct observation of the materials is impossible, therefore there has been a problem that it is difficult to apply the method for tilting the growing furnace in case of contacting the seed crystal and melt.
[Refer to : J.M. Parsey et al, J. Electrochem. Soc.
129, No. 2 (1982) 388]
As the other observing method, as shown in FIG. 1(C), though there has been known an observing method by utilizing an optical fiber bundle 11 of a system displaying on a monitor by taking photograph the whole growing process of a crystal 14 by utilizing vidicon camera through the lenses 12a, 12b and optical fiber bundle 11, this method has a problem because not only the cost of device becomes high, but also the state of the solid-liquid boundary interface is not observed distinctly, therefore this observing method is not utilized in general.
[Refer to : N.S. Kapany, Fiber Optics, Academic Press,
New York (1967)]